Smoke detectors are often built from low-cost components, for example LEDs, which in some cases differ significantly in terms of their characteristic properties (component scattering). Despite this, the sensitivity of all smoke detectors should be as similar as possible. This is not only relevant for use in the field, but, within certain limits, is also required by approval bodies. A smoke detector can, for example, be calibrated by immersing a scattering or reflecting object into the scattered light region, for example in that the immersed object is embodied as a diffuser, such as described in EP 0 658 264 B1.
A widely used method for calibrating smoke detectors is calibration in a so-called smoke channel in which, with regard to a throughput commensurate with mass production, typically a large number of smoke detectors are mounted on a carrier plate and tested jointly in the smoke channel. This gives rise to the problem that, due to turbulence and inhomogeneities in the distribution of the test aerosol flowing through the smoke channel, not all smoke detectors are exposed to the same aerosol conditions thus resulting in errors. Moreover, in particular due to the space required by smoke channels commonly used to date, calibration in a smoke channel is difficult to integrate into mass production.
A description entitled “Distributed Optical Smoke Sensor Calibration” from the UK company AW Technology Limited discloses a further method for testing smoke detectors. Herein, a scattered light sensor (smoke scatter sensor) is attached to a smoke channel in addition to the obscuration sensor always comprised thereby. This operates using a fan that conveys aerosol from the smoke channel into a sensor chamber of the scattered light sensor. The sensor chamber is connected to a channel in which one or more smoke detectors are located. Therefore, the smoke channel so-to-speak functions as an aerosol source for the volume flow conducted through the channel. Although, according to this description, calibration of the smoke detector is supposed to be possible, the manner in which calibration is to be performed is not described.